<%@page language="java" contentType="text/html;charset=utf-8" pageEncoding="utf-8"%>
<%@taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<html><body>
    <form action="${pageContext.request.contextPath}/welcome.jsp">
        <c:if test="${param.num1 != null}">
            name:<input type="text"name="num1">
            <input type="submit" value="submit"/><br\space />
        </c:if>
        <c:if test="${param.num1 == null}">
            <c:out value="${param.num1}"/><br/>
        </c:if>
</form>
</body></html>